Communications equipment, computers, work stations, automated test and production equipment, military targeting systems, home stereo systems, televisions, and other electronic devices as well as electrical loads using integrated circuits, solid state components, switching power supplies, semiconductor networks and the like, are increasingly characterized by small electrical contacts and miniature components which are very vulnerable to interference or damage due to interference from electrical disturbances carried by power line conductors connected thereto. Unpredictable variations in power line conductor voltage changes the operating range and can severely damage or destroy such devices. These devices and related process problems are very expensive to repair or to replace and therefore require cost-effective protection from transients and surges associated with the power.
High frequency disturbances can cause unreliable operation resulting in erroneous output. This "bad" output can be in the form of poorly machined metal to something as severe as unrecognizable transmitted information in various applications, including military applications.
Accordingly, the electrical art has included several devices for protecting sensitive communications and power installations, as well as other types of a-c loads, from damaging power surges and transients.
These devices are generally added on to a power distribution system. Examples of such "add on" devices are disclosed in patents such as U.S. Pat. No. 4,675,772 (the disclosure of which is incorporated herein by reference) and U.S. Pat. No. 4,835,650 (the disclosure of which s incorporated herein by reference). These devices are added to an already-existing wiring system by being connected to a main breaker panel which connects building wiring to utility power wiring, or by being connected to a subpanel located at or near a point of use, such as at a floor or other such building area.
While extremely effective, such add-on devices have the particular drawback of being subject to vagaries associated with installation. For example, while most electricians are highly competent, the inventors have found some installations to be out of the range set for specifications for proper installation, and some installations where the wiring was actually incorrectly connected. Such out of specification and erroneous wiring installations can vitiate, if not totally defeat, the overall results sought by the installation of such protection equipment.
Still further, the inventors have found that many electricians use long wires, which can be small in diameter, to connect the protection equipment to the various panels. Such wiring may be required due to the location and design of a particular panel; however, the inventors have found that such wiring, itself, can introduce errors into the equipment, and can defeat the overall results sought by the use of such protection equipment.
In addition, the inventors have found many cases where an electrician has not allowed for high neutral currents generated by multiple switching power supply loads or adequate provision for proper (isolated) grounding eventually traceable to a single system ground point which may even involve multiple panels.
Thus, no matter how proficient and competent the electrician, the connection of such protection equipment is often carried out in a manner which is not totally desirable for maximum effectiveness, and can vitiate the performance of such equipment.
Because light bulb and motor-type loads have neutral currents which are phasors that tend to sum to zero, many prior three-phase panels use a neutral bus which is sized for the same or smaller amperage as the phase supply connectors. This permits the neutral to be smaller and less expensive. However, computer loads (i.e., switching power supplies) are non-linear. They do not sum to zero on the neutral, but actually can sum to 3.sup.1/2 larger than the phase currents. Still further, many present panels have small lugs which necessitate the use of small wiring. Such small wiring may be a source of overheating, electrical noise or voltage drops. Therefore, many existing circuit breaker panels may prove to be inadequate to meet the needs of a modern multi-story building. As used herein, the term "panel" refers to well-known circuit breaker panels used to distribute electrical power to a multiplicity of electrical circuits or loads. These panels typically include buses (usually a flat metal structure) for each phase of supply power, a neutral or "return" bus and possible ground buses. Circuit breakers for each branch circuit to be distributed usually clamp or bolt onto the phase buses as a convenient means of physical attachment, electrical access and electrical protection.
Therefore, there is a need for a panel that can be used to connect electronic equipment to a source of power in a manner which permits efficient, effective and accurate connection of power surge protecting and filtering circuits into a building wiring system, and which can have the protection circuit and other performance enhancing elements installed at a factory.